Geochemical characteristics of dissolved inorganic carbon in the Changjiang estuary waters

Based on data collected from 29 stations including 2 anchor stations in the Changjiang Estuary, during field observation carried out from 19 to 26 May 2003, concentration, distribution and composition of dissolved inorganic carbon in the Changjiang Estuary waters were examined in this paper. All of the stations were established over two intersected transects identified as A and B. Transect A was in a downriver direction and transect B was along 122degrees19'E longitude. Results indicated that the distribution of HCO3-, CO32-, CO2 and DIC in a downriver direction all had a sharp horizontal concentration gradient. The gradients Of CO32- and CO2 appeared at the same position as the gradient of salinity, while those of HCO3- and DIC appeared several stations earlier than the gradient of salinity. Concentrations of HCO3-, CO32- and DIC increased along downriver direction, while it was reverse for CO2. Data of the stations located at transect B indicated that in most cases values of the 2 in above the bottom were higher than that on 0 in layer, especially for CO2, In the Changjiang Estuary waters, HCO3- accounted for 84.93 to 97.43% of the DIC with an average of 94.41 +/- 2.92%; CO32- accounted for 0.28 to 14.77% of the DIC with an average of 3.95 +/- 3.68%; CO2 accounted for 0.30 to 3.56% of the DIC with an average of 1.63 +/- 0.89%. Data of the two anchor stations indicated that all the four parameters fluctuated in a very large range during the investigated 48 hours. The spatial distribution characteristics of the four parameters were mainly influenced by the mixing of the freshwater and seawater. At the same time, other processes such as phytoplankton photosynthesis and decomposition of organic carbon also contributed to them to some extent. Factors influencing the temporal variations in such a short time scale were complicated and further research should be carried out.